Just days after a handful of new iMac customers received email notifications from Apple saying their credit cards had been charged and their 27-inch desktop computers were "Preparing for Shipment," many of those same customers reported receiving their newly redesigned 2012 iMacs in the mail on Wednesday.

"FedEx just came a day early!" wrote MacRumors user "califlorida" on Wednesday morning. "Busy day today but I will try to report back once I open and setup! Good luck to others getting them today!"

Considering how the online Apple Store still lists the 27-inch iMac as available to ship in January, many may be wondering how some customers are already receiving their new iMacs by Dec. 12. Customers have theorized that certain iMac configurations, perhaps the most basic options, may be easier for Apple to pack and ship than those with highly customized options.

The iMac purchased by customer "califlorida" actually has the highest-end customization options: His 27-inch iMac comes with a built-in 3.4 GHz i7 processor from Intel -- suped up for an extra $200 beyond the $1,999 tag -- and also comes with 1TB of storage space, in which he opted for Apple's new Fusion Drive. Even his graphics card was maxed out -- his iMac features a GeForce GTX 680MX from NVIDIA, which is the fastest GPU Apple offers -- it also costs hundreds more than Apple's top price listing.

"My order was completed by 3:08 AM EST on 11/30," Califlorida wrote. "So about 8 minutes after ordering went live. I had 2-3 day expedited shipping with original date of Dec. 21-28. Arriving 9 days early I'd say Apple was successful."

Given Califlorida's customer experience, it's possible that Apple is fulfilling the highest-end iMacs before trying to fulfill the simpler stock. Customers paid more for these computers, but given the degree of customization required to fulfill these iMac orders, it might be easier to get these out of the way before ramping up mass production of the simpler, more basic iMac models. Also, only U.S. customers have reported a status change in their orders, so it's possible that "country" was another filter in choosing which orders to fulfill first.

Apple first opened up pre-orders for the 27-inch iMac on Nov. 30, the same day the company released its 21.5-inch iMac to the public. Orders placed on that day listed 3-4 week waiting periods, but that changed on Dec. 7, when the 27-inch models started listing a "January" shipping date online.

The 27-inch iMac is roughly 20 inches tall, 26 inches wide and weighs about 21 pounds -- almost double the weight of the 21.5-inch iMac. The desktop features a 2560 x 1440 display resolution on its 27-inch (diagonally) IPS screen.

"Everything you see on the big, glossy display -- from skin tones and dark shadows to bright blue skies and green fields — is rich and vibrant," Apple says on its website. "And the colors are more true to life, too. That’s because every iMac display is individually color-calibrated using state-of-the-art spectroradiometers to match color standards recognized around the world."

The most basic 27-inch iMac is powered by a 2.9 GHz quad-core i5 processor from Intel, with Turbo Boost up to 3.6 GHz. The higher-end model features a 3.2 GHz quad-core i5 chip with 3.6 GHz Turbo Boost, but Apple will also configure custom models with the speedy 3.4 GHz i7 chip from Intel, which has a Turbo Boost up to 3.9 GHz.

From a graphics perspective, the 27-inch iMac is powered by GeForce GTX from NVIDIA -- the lower-end model has a 660M chip, while the higher-end desktop is powered by a 675MX graphics processor, but those customers can further choose to upgrade to a 680MX processor for enhanced performance.

The iMac comes with 1TB of storage, but customers can choose whether they'd like to upgrade to 3TB, also whether they'd like their storage to be flash, pure SSD, or a new mix of two that Apple calls the "Fusion Drive."

Apple’s new Fusion Drive contains 128 GB of flash storage with 1TB or 3TB HDD, which is fused into a single volume. With access to storage, the new Fusion Drive performs almost as well as Flash, but it keeps documents significantly more secure on the HDD.

“Apple has some logic, which figures out which apps you use the most and will shift those to the SDD,” explained Apple SVP of marketing Phil Schiller, at the company's iMac announcement on Oct. 23.

The 27-inch iMac also comes with two speakers on the bottom sides of the "chin," a 720p HD FaceTime camera and dual microphones and runs on OS X Mountain Lion.

As far as connectivity goes, the new iMac has an SDXC card slot, ports for USB 3.0 and Gigabit Ethernet, as well as two Thunderbolt ports for ultra-fast connections. The 2012 iMac is also supported by the latest 802.11n Wi-Fi technology and also supports Bluetooth 4.0 (also known as Smart Bluetooth) for near-instantaneous connections with accessories and peripherals such as the Magic Mouse and Wireless Keyboard.

Apple starts selling the basic 27-inch iMac at $1,799, but for $200 more, the computer will come with some faster graphics and computing processors. Further upgrades to the computer's specs are available after that $1,999 price tag.